A Read Only field in your Journey will be uneditable, and unclickable. Generally, you can tell a field is Read Only as it will be greyed out in your interface.
Read Only is similar to the Disabled control - with the main difference that this Control means the data will not be written back to the database.
An example of disabled fields in Loanapp are the following fields in the Setup section:
These fields a visible on screen, as they are important and should be able to be viewed by the user; but also disabled, as they are auto-populated from other systems and the user should not be able to edit them.
How to configure a field to be disabled
To make a field disabled, you need to make sure you are in Draft mode in Platform, find the field you want to make disabled, and scroll across to the Disabled Control: